Through the Fog: How Free Electrons Blur Ancient Light
Imagine looking at a distant mountain range through morning fog. The peaks' outlines are blurred, and if the fog is patchy, some slopes fade more than others. That's roughly how astronomers see the ancient light of the universe, which has been traveling to us for 13.8 billion years.
This light was born when the universe was just 380,000 years old, long before the first stars.